Method of reinforcing piston ring grooves

ABSTRACT

Method of making an aluminum alloy piston with a ring groove reinforcement wherein a grooved piston blank is cleaned to remove any oxide films, and a bonding metal is sprayed over the surface of the groove while the blank is at a temperature of from about 330* to 390* F., and thereafter a wear resistant metal is sprayed into the groove while the blank is still at a temperature within the aforementioned range to thereby fill the groove.

United States Patent 1191 Reinberger 1451 Feb. 13,1973

[54] METHOD OF REINFORCING PISTON 3,031,330 4/1962 Homick ..117/50 X NGGROOVES 3,033,705 5/1962 Hanink et a] ..1'17/50 3,04l,l l6 6/1962 Rosenet al ..277/189.5 [75] Inventor: William C. Reinberger, lndepen-3,295,198 1/1967 Coan 1 1 ..29/l56.5 R X dence, Ohio 3,405,610 10/1968Hill et al. ..29/l56.5 R X [73] Assrgnee: TRW Inc., Cleveland, OhioPrimary Exami'ier charles w Lanham [22] Filed: Jan. 13, 1971 AssistantExaminer-Victor A. Dipalma [2]] Appl NW 106,279 Attorney-Hill, Sherman,Meroni, Gross & Simpson Related US. Application Data ABSTRACT [63]Continuation-impart of Ser. No. 762,720, Sept. 26, Method of making analuminum alloy piston with a 1968, abandoned, ring groove reinforcementwherein a grooved piston blank is cleaned to remove any oxide films, anda [52] 0.8. CI. ..29/ 6.5 R, 117/50, 117/105, ing metal is pr y r hSurface f h 277/1395 groove while the blank is at a temperature of from[51] Int. Cl. .1523, 15/10 ut 3 to 3 and thereafter a wear resistant[58] Field at Search. ..29/156,5, 5212,5274, 527 6; metal is sprayedinto the groove while the blank is still 117/50, 31, 92/223, 222; 277/189.5 at a temperature within the aforementioned range to thereby tillthe groove. 56 References C't d 1 I e 6 Claims, 4 Drawing Figures UNITEDSTATES PATENTS 2,833,668 5/1958 Dailey et al. ..l17/5O METHOD OFREINFORCING PISTON RING GROOVES CROSS REFERENCE TO RELATED APPLICATIONThis application is a continuation-in-part of my copending applicationentitled Method of Reinforcing piston Ring Grooves U.S. Ser. No. 762,720filed Sept. 26, 1968, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention isin the field of reinforcing ring grooves in aluminum alloy pistons by asequence of operations including preheating the piston blank, gritblasting the blank in the area of the grooves to remove any existingoxide film and to roughen the surface, after which the temperature ofthe blank is adjusted to a value between about 330 and 390 F., whereupona bonding metal is sprayed into the grooves, followed substantiallyimmediately by spraying a wear resistant metal such as stainless steelinto the grooves.

2. Description of the Prior Art Heavy duty internal combustion enginesusing aluminum alloy pistons are subject to the difficulty that thewalls of the piston ring groove are liable to deformation in use so thatreinforcement of the ring groove area has become a necessity. In somecases, this reinforcement has taken the form of an insert which isusually metallurgically bonded to the metal of the piston head. Examplesof this type of structure will be found in Stevens US. Pat. No.2,550,879; Daub US. Pat. No. 3,118,712; and Christen et al. US. Pat. No.3,183,796.

Other attempts at reinforcement have centered on the technique ofspraying a reinforcing metal into the preformed groove. An example ofthis type of procedure will be found in Dailey et al. U.S. Pat. No.2,833,668.

,The present invention is concerned with the second of the techniquesmentioned above, that of spraying a wear resistant metal into a groovewhich has been preformed in the head of the piston. With the sequence ofoperations to be described more fully in a succeeding portion of thisdisclosure, it has been found possible to provide such a reinforcementat'a significantly lower cost than heretofore encountered, and at thesame time it is now possible to increase the strength of the bondbetween the piston alloy and the sprayed metal.

SUMMARY OF THE INVENTION In the method of the present invention, analuminum alloy piston is first provided with a peripheral groove of astepped configuration. Next, the grooved piston is preheated at atemperature of about 400 F., but below the softening temperature of themetal of the piston alloy blank. While the piston blank is still at amoderately elevated temperature by virtue of the preheat, the groove issubjected to grit blasting to remove any oxides which would otherwiseinterfere with the bonding operation and to simultaneously roughen thesurface. The next step consists of spraying on a bonding metal over thesurface of the groove while the blank is still at a temperature of about300 to 390 F. 1m mediatelythereafter, a wear resistant metal such asstainless steel is sprayed into the groove over the thin BRIEFDESCRIPTION OF THE DRAWINGS Other objects, features and advantages ofthe invention will be readily apparent from the following description ofcertain preferred embodiments thereof, taken in conjunction with theaccompanying drawings, although variations and modifications may beeffected without departing from the spirit and scope of the novelconcepts of the disclosure, and in which:

FIG. 1 is a fragmentary view of a portion of the head of the pistonblank with a peripheral groove machined therein;

FIG. 2 is a somewhat schematic illustration of the manner in which thegroove is grit blasted;

FIG. 3 is another somewhat schematic view illustrating the manner inwhich the metal spraying operations can be used to provide both thebonding metal and the wear resistant metal in the groove; and

FIG. 4 is a view similar to FIG. 1, but showing the head of the pistonafter the machining operation has been completed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 10indicates generally a piston blank composed of an aluminum alloy. Thehead of the piston is first provided with a peripheral groove 11 whichin the form of the invention illustrated, has a stepped profile. Whilethe configuration of the groove can take various forms, there arecertain considerations which dictate the use of the stepped-typeprofile. For one,'the cost of the sprayed meta'l inlay should be kept aslow as possible, so that the volume and the maximum thickness of thesprayed metal should be held to a minimum consistent with the requiredphysical properties. By holding the thickness of the deposit to .aminimum, the residual stress level in the deposited metal is alsominimized.

The minimum thickness of sprayed metal on each side of the ring groovemust be great enough to support the loads imposed by the piston ring.The sprayed metal must extend into the groove to a depth that willprovide a wear resistant surface over the area where the'ring loading ismost severe. From experience, it has been determined that pistons forheavy duty engines require a sprayed metal reinforcement with a minimumthickness of about 0.060 to 0.100 inch over the outer one-half totwo-thirds of the ring groove depth.

The groove should be so shaped as to avoid tension loads on the bondbetween the sprayed metal and the piston alloy. Since the gas pressureloads and the friction loads on the piston ring are parallel to the axisof the piston, the groove should be designed with surfaces both parallelto and perpendicular to the center line of the piston. The resultingperpendicular surfaces of the groove should be joined by a small radiussince sprayed metal particles tend to bridge across a sharp corner andleave an undesirable void.

In the ideal situation, sprayed metal would be applied normal to thesurface of the aluminum piston alloy to insure the best possible bond.However, because of the other requirements mentioned, this idealsituation is not capable of realization. Consequently, the groove widthwith respect to its depth should therefore be established to permit thesprayed metal particles to impinge upon all surfaces of the steppedgroove at an angle of approximately 45 from the normal.

After the peripheral groove 11 had been machined into the head of thepiston blank, the piston blank is washed to remove all oils and residue.Various degreasing solvents such as trichlorethylene can be used forthis purpose. The washing prevents contamination of the grit and gritblasting equipment used in the subsequent operation, and insures a cleansurface for receiving the sprayed metal.

The next step in the process consists in preheating the workpiece to atemperature of about 400 F., but below the softening point of the metalto remove all residual moisture and to prevent the formation of acondensate in the subsequent operation. For aluminum alloy pistons, thispreheat temperature is preferably in the range from about 400 to 420F.

The next step of the process, illustrated in FIG. 2 of the drawings,consists in grit blasting the surfaces of the groove. Asillustrated inFIG. 3, the grit may be applied through a pair of nozzles 12 and 13disposed on opposite sides of the blank. During the grit blastingoperation, the piston blank is mounted on a suitable turntable rotatedat a relatively slow speed about 75 revolutions per minute. The pistonblank groove is blasted on both sides simultaneously at an angle of 45from the normal to all surfaces of the stepped groove. The blast iscontinued until a satiny finish of maximum uniform roughness on allsurfaces of the groove is achieved.

While the piston blank is still hot from the preheat, and at atemperature in the range from about 330 to 390 F., the bond coat issprayed onto the groove by means of a metallizing gun 14 while the blankis oscillated to fill the groove completely, as illustrated by thedashed lines in FIG. 3. I particularly prefer to use a bond coatconsisting of nickel aluminide since this material forms a non-porouscoating which is resistant to gaseous atmospheres up to about 3,200 F.

The preferred coating thickness for the bonding layer is about 0.004 to0.006 inch.

Nickel aluminide coatings can be produced from commercial materialswhich are formed of composite particles in the form of a wire. Thecomposite particles are formed by chemically depositing nickel ontoaluminum particles. When fused and sprayed, there is an exothermicreaction with the formation of nickel aluminide. The nickel aluminide isself-bonding to properly prepared surfaces, and no subsequent fusiontreatment is required.

The next step consists in spraying the wear resistant metal to fill thegroove 11 while the piston blank is still hot. In this operation, theworkpiece should still be a temperature of about at least 330 to 390 F.to minimize the residual stress level in the sprayed metal inlay whenthermal equilibrium is established. The application of the wearresistant inlay can be made with the same type of apparatus asillustrated in FIG. 3m

provide complete coverage throughout the depth of the groove. During thespraying of the wear resistant metal if it becomes necessary to cool thepiston blank to avoid exceeding 390 F., a cooling air jet can bedirected on the inner surfaces of the piston.

Finally, the piston is machined to remove excess reinforcement metal andto trim the piston to final dimensions. The final step consists inmachining a groove 16 in the reinforcement metal for receiving thepiston ring.

The following specific example illustrates with more particularity theprocess conditions under which the process of the present invention canbe best carried out.

EXAMPLE An aluminum alloy piston blank is provided with a groove of thetype shown in FIG. 1 of the drawings. After washing to remove oils andresidue, the piece was preheated to a temperature of 400 F. to removeall residual moisture and prevent the formation of condensate.

While the piece was hot, it was grit blasted using a cast iron grit at apressure of 80 pounds psi while the piece was rotated on a horizontalturntable at a speed of 75 revolutions per minute. The piece wasfixtured on the turntable so that both sides of the groove could beblasted simultaneously at an angle of 45 from the normal to all surfacesof the stepped groove. The blasting was continued for 8 seconds at aspacing of 3 inches between the nozzles and the workpiece at point ofcontact.

Immediately after the grit blasting, and while the temperature of thepiece was still above 325 F., a nickel aluminide bond coat was applied.The workpiece was mounted in the fixture and rotated at 125 rpm. Astandard Metco" metallizing gun was used, using a one-eighth inchdiameter wire. The gun was positioned 4 inches from the surface to becoated. The acetylene pressure was set at 17 psi and the oxygen pressurewas set at 50 psi. Gun settings for the metallizing gun were adjusted toprovide air at psi and 43 cubic feet per hour, oxygen at 40 to 42 psiand 42 cubic feet per hour, acetylene at 12 to 14 psi and 34 cubic feetper hour, using a wire speed of 3 feet per minute. The workpiece wasoscillated from side to side through an included angle of for 9 secondsat approximately I second intervals causing the sprayed metal to impingeon first one side of the groove and then on the other. The bond coatingthickness which resulted averaged about 0.005 inch.

The groove was filled with a stainless steel spray coating using thesame fixture and spray gun as used in providing the bond coat. Theworkpiece at this stage should still have a temperature of at least 330F., but not more than 390 F. The gun was positioned 4 inches from thesurface to be coated. The gun settings were such that the air pressurewas 55 pounds psi and 40 cubic feet per hour. The oxygen setting-wassuch that the pressure was 30 to 34 psi with a volumetric rate of 37cubic feet per hour. The acetylene was introduced under a pressure of 15pounds psi with a volume rate of 37.5 cubic feet per hour. The wirespeed was 4.5 feet per minute for a one-eighth inch wire diameter. Theworkpiece was oscillated through an included angle of 60 starting withspraying the left side of the groove for 5 seconds followed by the rightside of the groove for 5 seconds. This sequence was repeated for twoadditional 5 second intervals. Then the left side was sprayed for 30seconds, followed by spraying the right side for the same interval oftime. Then the spray was allowed to dwell on the center of the groovefor a period of 100 seconds. Next, the left side was sprayed for secondsfollowed by an equal amount of spraying on the right side. The sprayingwas completed by training the gun on the center of the groove for 35seconds or as long as required to completely fill the groove. Duringthis spraying of the stainless steel, a cooling air jet was played onthe inner surfaces of the piston to prevent the temperature of thepiston from exceeding 390 F.

FInally, the piston was given a finished machining operation in theusual way, using a relatively light cutting tool pressure to machine thepiston ring groove in the sprayed metal inlay.

Operation of the process in the manner stated in the example has beenfound to reduce the cost of applying the sprayed metal, and also hasresulted in a 30 percent increase in the strength of the bond betweenthe piston alloy and the sprayed metal, as compared with previouspractices.

A series of tests was run to determine the tensile strength of stainlesssteel inlays versus blank temperature at the start of the metal sprayoperation. In one series of tests, spraying of the blank while the blankwas at a temperature of about 120 F. resulted in a tensile strength ofabout 17,800 psi. When the temperature of the blank at the time ofspraying was increased to 190 F., the resulting tensile strength was18,100 psi. However, when the blank temperature was raised to 330 F.,the tensile strength rose to 22,700 psi. When the blank temperature wasincreased to 365 F., the tensile strength was 24,000 psi. When the blanktemperature was 390 F., the resulting tensile strength was 23,300 psi.At blank temperatures in excess of 400 F., specifically at 420 and 470F., the tensile strength dropped to below 21,500 psi.

In another series of tests, using a different type of aluminum alloyblank, maintaining the blank at a temperature of F., resulted in atensile strength of 20,400 psi for the stainless steel inlay. When theblank temperature was increased to F., the tensile strength increasedonly to 21,000 psi. At a blank temperature of 330, however, the tensilestrength rose sharply to 23,200 psi, while using a blank temperature of360 F., resulted in achieving a tensile strength in excess of 26,500psi. At a blank temperature of 390 F., the tensile strength was still inexcess of 25,000 psi. However, when operating at a blank temperature of460 F., the resulting tensile strength fell below 24,000 ps1.

I claim as my invention:

1. The method of making an aluminum alloy piston with a ring groovereinforcement which comprises providing a piston blank having aperipheral groove formed therein, heating said blank to a temperature inthe range from 330 to 390 F., spraying a bonding metal over the surfaceof said groove while the temperature of the blank is in said range, andthereafter spraying a wear resistant metal into said groove to fill thesame while said blank is at a temperature within said range.

27 The method of claim 1 1n Wl'lllCh said wear resistant metal isstainless steel.

3. The method of claim 1 in which said wear resistant metal is nickelaluminide.

4. The method of claim 1 which includes the steps of heating said blankto an elevated temperature between 400 F. and the softening point of theblank, and grit blasting said groove while said blank is at saidelevated temperature prior to spraying on said bonding metal.

5. The method of claim 1 in which said groove has a stepped profile.

6. The method of claim 1 in which said blank is oscillated duringapplicationof said bonding metal and said wear resistant metal.

1. The method of making an aluminum alloy piston with a ring groovereinforcement which comprises providing a piston blank having aperipheral groove formed therein, heating said blank to a temperature inthe range from 330* to 390* F., spraying a bonding metal over thesurface of said groove while the temperature of the blank is in saidrange, and thereafter spraying a wear resistant metal into said grooveto fill the same while said blank is at a temperature within said range.2. The method of claim 1 in which said wear resistant metal is stainlesssteel.
 3. The method of claim 1 in which said wear resistant metal isnickel aluminide.
 4. The method of claim 1 which includes the steps ofheating said blank to an elevated temperature between 400* F. and thesoftening point of the blank, and grit blasting said groove while saidblank is at said elevated temperature prior to spraying on said bondingmetal.
 5. The method of claim 1 in which said groove has a steppedprofile.